How strict are formal postbacc

Depends on what programs you are looking at. I don't know of any program that will waive their standards based on your most recent academic success, however an upward trend is a good thing. Perhaps you should finish strong on your own and look into other options like special masters programs that are geared towards those who have completed thieir requirements however still fall below numerical standands for most med schools and want to prove they can handle more rigorous coursework by entering these one year programs.